Polychlorinated biphenyls (PCBS) and the DDT/DDE (DDE is the stored metabolite of DDT) family are toxic, widespread pollutants. Both pass from mother to child through the placenta and by contaminating breast milk. This project includes a study of subjects exposed to low levels of both compounds in North Carolina, a study in Mexico where levels of DDE are two to five times higher, and a study of persons poisoned by PCBs in Taiwan. In North Carolina, we had reported that children who were exposed to the upper 5-10 percent of background PCB levels while in utero had detectable motor delay up to 2 years of age, but we were unable to find motor or cognitive delay out to school age. We also found that breast fed children scored slightly higher on developmental tests at all ages, irrespective of PCB or DDE levels. Since PCBs can cause long term induction of drug and steroid metabolizing enzymes in animals, we are planning to look at onset of puberty in this cohort. Using a mathematical model of the effect of breast feeding on post perinatal mortality, we showed that programs aimed at preventing HIV+ women from breastfeeding must have very little impact on breastfeeding rates overall if they are to minimize mortality. We have completed field work on a study in Mexico in which we look at lactation failure in women with high levels of DDE in milk. In Taiwan, an epidemic of 2000 cases of PCB poisoning occurred in 1979. We are planning a study of mortality in the cohort at twelve years of follow-up.